This application claims the benefit of U.S. Provisional Application No. 60/364,683, filed Mar. 15, 2002 and entitled SILICON-BASED LIGHT EMITTING DIODE, which is in its entirety incorporated herewith by reference.
The invention relates to an apparatus and method for emitting light. The invention also relates more particularly to a silicon-based light-emitting diode for emitting light that may include wavelengths in the ultraviolet portion of the electromagnetic spectrum.
Light emitting diodes, or LEDs, are known per se. Conventional LEDs utilize the semiconducting properties of materials such as silicon.
In a conventional LED, light is generated when free electrons drop from the conduction band of a semiconducting diode into energy holes. Each such event releases energy in the form of a photon, with the wavelength of the photon depending upon the energy gap between the conduction band and the holes. As the energy gap becomes larger, the photons released likewise become more energetic. The more energy an individual photon has, the shorter its wavelength.
The principles governing the operation of conventional LEDs are well known, and are not further described herein.
However, known LEDs suffer from several limitations.
For example, the wavelengths that may be produced are limited by the magnitude of the energy gap. The shorter the wavelength of light that is to be emitted, the larger the energy gap must be. It is therefore particularly difficult to produce light with short wavelengths, in particular ultraviolet light, using known LEDs. In principle, it is possible to produce a semiconducting LED with an energy gap large enough that it emits ultraviolet light, i.e. light having a wavelength of less than about 400 nm. However, such LEDs are difficult to produce, expensive, and inefficient.
Indeed, silicon-based LEDs are extremely inefficient emitters of light in general. The best reported efficiency for a silicon-based LED of conventional design is 0.8%. That is, no more than 0.8% of the energy applied to that LED is emitted as light, the remainder typically being lost as heat.
It is the purpose of the present invention to overcome these difficulties, thereby providing an improved apparatus and method for generating light, including but not limited to ultraviolet light.
It is more particularly the purpose of the present invention to provide an LED that is suited for producing light in wavelengths that may include the ultraviolet portion of the electromagnetic spectrum, and a method for producing the same.
An embodiment of an LED in accordance with the principles of the present invention includes a substrate. A first conductive layer is disposed on a first side of the substrate.
An insulating layer is disposed on a second side of the substrate. The insulating layer defines a plurality of microcavities therein. The microcavities have small points, referred to herein as asperites, on their surfaces. In addition, the microcavities contain gas therein.
A second conductive layer is disposed over the insulating layer. The second conductive layer is transparent to radiation of the frequency that the diode emits.
When an electrical potential is applied between the first conductive layer and the second conductive layer, the microcavities in the insulating layer act as tiny gas discharge lamps.
This occurs because the high electrical resistance of the insulating layer allows strong electric fields to develop within the microcavities. As these strong electric fields develop, the sharp tips of the asperites begin to eject electrons, ionizing the gas present in the microcavities. The gas transforms into plasma, which radiates light at one or more plasma emission lines.
By controlling the physical properties of the device, i.e. the composition and pressure of the gas in the microcavities, it is possible to control the frequency of the light emitted. For example, under the proper conditions, the light is in the ultraviolet portion of the spectrum.
It is emphasized that an LED in accordance with the principles of the present invention does not rely on semiconductive properties such as electron transport.
It is furthermore emphasized that although particular embodiments of an LED in accordance with the principles of the claimed invention may produce ultraviolet light, the invention is not limited only to embodiments that produce ultraviolet light. Other embodiments may produce other wavelengths.
An LED in accordance with the principles of the present invention may be incorporated into an LED assembly.
An LED assembly in accordance with the principles of the present invention includes an LED, with an encapsulation enclosing it. The encapsulation has a window that is transparent to the wavelength of the light that is emitted by the LED. The assembly also includes first and second contact pins that are electrically connected to the first and second conductive layers. Thus, an electrical potential applied to the contact pins causes an electrical potential to be applied to the first and second conductive layers, so that the LED then emits light.
In a method for producing an LED in accordance with the principles of the present invention, a suitable substrate is provided. A first conductive layer is applied to a first side of the substrate.
The second side of the substrate is etched to form an insulating layer with microcavities therein, the microcavities having asperites.
A second conductive layer, transparent to radiation of the wavelength that the LED is to produce, is applied over the insulating layer.
The microcavities are impregnated with gas.
An LED in accordance with the principles of the present invention may be incorporated into an LED assembly.
In a method for producing an LED assembly in accordance with the principles of the present invention, an LED is provided.
The LED is encapsulated with an encapsulation. The encapsulation has a window that is transparent to radiation of the wavelength emitted by the LED.
A first contact pin is connected electrically to the first conductive layer, and a second contact pin is connected electrically to the second conductive layer.